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2. hallucination
Medical Encyclopedia:
Hallucinations
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Home > Library > Health > Medical Encyclopedia
More about
Hallucinations:
Causes and symptoms
Diagnosis
Treatment
Prognosis
Resources
Definition
Hallucinations are false or distorted sensory experiences that appear to be real
perceptions. These sensory impressions are generated by the mind rather than by any
external stimuli, and may be seen, heard, felt, and even smelled or tasted.
Description
A hallucination occurs when environmental, emotional, or physical factors such as stress,
medication, extreme fatigue, or mental illness cause the mechanism within the brain that
helps to distinguish conscious perceptions from internal, memory-based perceptions to
misfire. As a result, hallucinations occur during periods of consciousness. They can
appear in the form of visions, voices or sounds, tactile feelings (known as haptic
hallucinations), smells, or tastes.
Patients suffering from dementia and psychotic disorders such as schizophrenia
frequently experience hallucinations. Hallucinations can also occur in patients who are
not mentally ill as a result of stress overload or exhaustion, or may be intentionally
induced through the use of drugs, meditation, or sensory deprivation. A 1996 report,

3. published in the British Journal of Psychiatry, noted that 37% of 4,972 people surveyed
experienced hypnagogic hallucinations (hallucinations that occur as a person is falling to
sleep). Hypnopomic hallucinations (hallucinations that occur just upon waking) were
reported by 12% of the sample.
— Paula Anne Ford-Martin
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hallucination
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Dictionary: hal·lu·ci·na·tion (hə-lū'sə-nā'shən)
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Home > Library > Literature & Language > Dictionary

4. n.
1.
a. Perception of visual, auditory, tactile, olfactory, or gustatory experiences
without an external stimulus and with a compelling sense of their reality,
usually resulting from a mental disorder or as a response to a drug.
b. The objects or events so perceived.
2. A false or mistaken idea; a delusion.
hallucinational hal·lu'ci·na'tion·al or hal·lu'ci·na'tive adj.
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Britannica Concise Encyclopedia:
hallucination
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Home > Library > Miscellaneous > Britannica Concise Encyclopedia
Perception of objects, sounds, or sensations having no demonstrable reality, usually
arising from a disorder of the nervous system or in response to certain drugs (see
hallucinogen). Hallucinations are in many ways similar to dreams: they derive their
content from perceptions known to memory, though these can be greatly transformed.
Hallucinations can result when attention collapses from intense arousal due to extreme
anxiety, fatigue, excitement, or other causes. They figure prominently in the diagnosis of
schizophrenia.
For more information on hallucination, visit Britannica.com.
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Neurological Disorder:

5. Hallucination
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Home > Library > Health > Neurological Encyclopedia
Definitions
A hallucination is a sensory perception without a source in the external world. The
English word "hallucination" comes from the Latin verb hallucinari, which means "to
wander in the mind." Hallucinations can affect any of the senses, although certain
diseases or disorders are associated with specific types of hallucinations.
It is important to distinguish between hallucinations and illusions or delusions, as the
terms are often confused in conversation and popular journalism. A hallucination is a
distorted sensory experience that appears to be a perception of something real even
though it is not caused by an external stimulus. For example, some elderly people who
have been recently bereaved may have hallucinations in which they "see" the dead loved
one. An illusion, by contrast, is a mistaken or false interpretation of a real sensory
experience, as when a traveler in the desert sees what looks like a pool of water, but in
fact is a mirage caused by the refraction of light as it passes through layers of air of
different densities. The bluish-colored light is a real sensory stimulus, but mistaking it for
water is an illusion. A delusion is a false belief that a person maintains in spite of
evidence to the contrary and in spite of proof that other members of their culture do not
share the belief. For example, some people insist that they have seen flying saucers or
unidentified flying objects (UFOs) even though the objects they have filmed or
photographed can be shown to be ordinary aircraft, weather balloons, satellites, etc.
Description
It would be difficult to describe a "typical" hallucination, as these experiences vary
considerably in length of time, quality, and sense or senses affected. Some hallucinations
last only a few seconds; however, some people diagnosed with Charles Bonnet syndrome
(CBS) have reported visual hallucinations lasting over several days, while people who
have taken certain drugs have experienced hallucinations involving colors, sounds, and
smells lasting for hours. Albert Hoffman, the Swiss chemist who first synthesized
lysergic acid diethylamide (LSD), experienced nine hours of hallucinations after taking a
small amount of the drug in 1943. In 1896, the American neurologist S. Weir Mitchell
published an account of the six hours of hallucinations that followed his experimental
swallowing of peyote buttons.
There is not always a close connection between the cause of a person's hallucinations and
the emotional response to them. One study of patients diagnosed with CBS found that
30% of the patients were upset by their hallucinations, while 13% found them amusing or
pleasant. The environment in which LSD and other hallucinogens are taken may affect an
individual's psychological constitution and personal reactions. The writer Peter
Matthiessen, for example, noted that his 1960s experiences with LSD "were magic

6. shows, mysterious, enthralling," while his wife "… freaked out; that is the drug term, and
there is no better.… her armor had cracked, and all the night winds of the world went
howling through." In contrast to those who take hallucinogens, however, a majority of
patients with narcolepsy, alcoholic hallucinosis, or post-traumatic disorders finds their
hallucinations frightening.
Demographics
The demographics of hallucinations vary depending on their cause; however, many
researchers think that they are underreported for several reasons:
• Fear of being thought "crazy" or mentally ill
• Gaps in research. For example, some types of hallucinations are associated with
disorders that primarily affect the elderly, who are often underrepresented in
health surveys
• Fear of being reported to law enforcement for illegal drug use
In 2000, one of the few studies of hallucinations in a general Western population reported
the following statistics:
• Of a total sample of 13,000 adults, 38.7% reported hallucinations: 6.4% had
hallucinations once a month, 2.7% once a week, and 2.4% more than once a
week.
• Of the subjects, 27% reported having hallucinations in the daytime. In this group,
visual (3.2%) and auditory (0.6%) hallucinations were closely associated with
diagnoses of psychotic or anxiety disorders.
• Of the subjects, 3.1% reported haptic (tactile) hallucinations; most of these
subjects were current drug users.
There is currently no evidence that hallucinations occur more frequently in some racial or
ethnic groups than in others. In addition, gender does not appear to make a difference.
The demographics of hallucinations associated with some specific age groups, conditions,
or disorders are as follows:
• Children. Hallucinations are rare in children below the age of eight. About 40% of
children diagnosed with schizophrenia, however, have visual or auditory
hallucinations.
• Eye disorders. About 14% of patients treated in eye clinics for glaucoma or age-
related macular degeneration report visual hallucinations.
• Alzheimer's disease (AD). About 40–50% of patients diagnosed with AD develop
hallucinations in the later stages of the disease.
• Drug use. Hallucinogens are the third most frequently abused class of drugs (after
alcohol and marijuana) among high school and college students. Various surveys
report that about 7% of people in the United States over the age of 12 have taken
LSD at least once; that 5% of high school seniors admit to using MDMA

7. (Ecstasy); and that 20–24% of college students use MDMA. The highest rate of
hallucinogen abuse is found in Caucasian males between the ages of 18 and 25.
• Normal sleep/wake cycles. Sleep researchers in Great Britain and the United
States have reported that 30–37% of adults experience hypnagogic hallucinations,
which occur during the passage from wakefulness into sleep, while about 10–12%
report hypnopompic hallucinations, which occur as a person awakens.
Hallucinations related to ordinary sleeping and waking are not considered an
indication of a mental or physical disorder.
• Migraine headaches. About 10% of patients diagnosed with migraine headaches
experience visual hallucinations prior to the onset of an acute attack.
• Adult-onset schizophrenia. According to the National Institute of Mental Health
(NIMH), about 75% of adults diagnosed with schizophrenia experience
hallucinations, most commonly auditory or visual. The auditory hallucinations
may be command hallucinations, in which the person hears voices ordering him
or her to do something. For example, the man who killed a Swedish politician in
September 2003 told the police that voices in his head told him "to attack."
• Temporal lobe epilepsy (TLE). About 80% of patients diagnosed with TLE report
gustatory and olfactory hallucinations as well as auditory and visual
hallucinations.
• Narcolepsy. Frequent hypnagogic hallucinations are considered one of four
classic symptoms of narcolepsy, and are experienced by 60% of patients
diagnosed with the disorder.
• Post-traumatic stress disorder (PTSD). Studies of combat veterans diagnosed with
PTSD have found that 50–65% have experienced auditory hallucinations. Visual,
olfactory, and haptic hallucinations have been reported by survivors of rape and
childhood sexual abuse.
Causes
The neurologic causes of hallucinations are not currently completely understood,
although researchers have identified some factors in the context of specific disorders, and
have proposed various hypotheses to explain hallucinations in others. There does not
appear to be a single causal factor that accounts for hallucinations in all people who
experience them.
Sleep deprivation
Research subjects who have undergone sleep deprivation experiments typically begin to
hallucinate after 72–96 hours without sleep. It is thought that these hallucinations result
from the malfunctioning of nerve cells within the prefrontal cortex of the brain. This area
of the brain is associated with judgment, impulse control, attention, and visual
association, and is refreshed during the early stages of sleep. When a person is sleep-
deprived, the nerve cells in the prefrontal cortex must work harder than usual without an
opportunity to recover. The hallucinations that develop on the third day of wakefulness
are thought to be hypnagogic hallucinations that occur during "microsleeps," or short
periods of light sleep lasting about one to ten seconds.

8. Post-traumatic memory formation
Hallucinations in trauma survivors are caused by abnormal patterns of memory formation
during the traumatic experience. In normal situations, memories are formed from sensory
data, organized in a part of the brain known as the hippocampus, and integrated with
previous memories in the frontal cortex. People then "make sense" of their memories
through the use of language, which helps them to describe their experiences to others and
to themselves. In traumatic situations, however, bits and pieces of memory are stored in
the amygdala, an almond-shaped structure in the brain that ordinarily attaches emotional
significance to memories, without being integrated by the hippocampus and interpreted in
the frontal cortex. In addition, the region of the brain that governs speech (Broca's area)
often shuts down under extreme stress. The result is that memories of the traumatic event
remain in the amygdala as a chaotic wordless jumble of physical sensations or sensory
images that can re-emerge as hallucinations during stressful situations at later points in
the patient's life.
Irritative hallucinations
In 1973, a British researcher named Cogan categorized hallucinations into two major
groups that he called "irritative" and "release" hallucinations. Irritative hallucinations
result from abnormal electrical discharges in the brain, and are associated with such
disorders as migraine headaches and epilepsy. Brain tumors and traumatic damage to the
brain are other possible causes of abnormal electrical activity manifesting as visual
hallucinations.
Hallucinations have also been reported with a number of infectious diseases that affect
the brain, including bacterial meningitis, rabies, herpes virus infections, Lyme disease,
HIV infection, toxoplasmosis, Jakob-Creuzfeldt disease, and late-stage syphilis.
Release hallucinations
Release hallucinations are most common in people with impaired eyesight or hearing.
They are produced by the spontaneous activity of nerve cells in the visual or auditory
cortex of the brain in the absence of actual sensory data from the eyes or ears. These
experiences differ from the hallucinations of schizophrenia in that those patients
experiencing release hallucinations are often able to recognize them as unreal. Release
hallucinations are also more elaborate and usually longer in duration than irritative
hallucinations. The visual hallucinations of patients with CBS are an example of release
hallucinations.
Neurotransmitter imbalances
Neurotransmitters are chemicals produced by the body that carry electrical impulses
across the gaps (synapses) between adjoining nerve cells. Some neurotransmitters inhibit
the transmission of nerve impulses, while others excite or intensify them. Hallucinations
in some conditions or disorders result from imbalances among these various chemicals.

9. NARCOLEPSY Narcolepsy is a disorder characterized by uncontrollable brief episodes
of sleep, frequent hypnagogic or hypnopompic hallucinations, and sleep paralysis.
Between 1999 and 2000, researchers discovered that people with narcolepsy have a much
lower than normal number of hypocretin neurons, which are nerve cells in the
hypothalamus that secrete a neurotransmitter known as hypocretin. Low levels of this
chemical are thought to be responsible for the daytime sleepiness and hallucinations of
narcolepsy.
PRESCRIPTION MEDICATIONS Hallucinations have been reported as side effects of
such drugs as ketamine (Ketalar), which is sometimes used as an anesthetic but has also
been used illegally to commit date rape; paroxetine (Paxil), an SSRI antidepressant;
mirtazapine (Remeron), a serotonin-specific antidepressant; and zolpidem (Ambien), a
sleep medication. Ketamine prevents brain cells from taking up glutamate, a
neurotransmitter that governs perception of pain and of one's relationship to the
environment. Paroxetine alters the balance between the neurotransmitters serotonin and
acetylcholine.
Hallucinations in patients with Alzheimer's disease are thought to be a side effect of
treatment with neuroleptics (antipsychotic medications), although they may also result
from inadequate blood flow in certain regions of the brain. The antiretroviral drugs used
to treat HIV infection may also produce hallucinations in some patients.
HALLUCINOGENS AND DRUGS OF ABUSE Like the hallucinations caused by
prescription drugs, hallucinations caused by drugs of abuse result from disruption of the
normal balance of neurotransmitters in the brain. Hallucinations in cocaine and
amphetamine users, for example, are associated with the overproduction of dopamine, a
neuro-transmitter associated with arousal and motor excitability. LSD appears to produce
hallucinations by blocking the action of the neurotransmitters serotonin (particularly
serotonin-2) and norepinephrine. Phencyclidine (PCP) acts like ketamine in producing
hallucinations by blocking the reception of glutamate.
People who have used LSD sometimes experience flashbacks, which are spontaneous
recurrences of the hallucinations and other distorted perceptions caused by the drug.
Some doctors refer to this condition as hallucinogen persisting perception disorder, or
HPPD.
There are two types of alcohol withdrawal syndromes characterized by hallucinations.
Alcoholic hallucinosis typically occurs after abrupt withdrawal from alcohol after a long
period of excessive drinking. The patient hears threatening or accusing voices rather than
"seeing things," and his or her consciousness is otherwise normal. Delirium tremens
(DTs), on the other hand, is a withdrawal syndrome that begins several days after
drinking stops. A patient with the DTs is disoriented, confused, depressed, feverish, and
sweating heavily as well as hallucinating, and the hallucinations are usually visual.
MOOD DISORDERS Visual hallucinations occasionally occur in patients diagnosed
with depression, particularly the elderly. These hallucinations are thought to result from

10. low levels of the neurotransmitter serotonin. The hallucinations that occur in patients
with Parkinson's disease appear to result from a combination of medication side effects,
depressed mood, and impaired eyesight.
Schizophrenia
The auditory hallucinations associated with schizophrenia may be the end result of a
combination of factors. These hallucinations have sometimes been attributed to unusually
high levels of the neurotransmitter dopamine in the patient's brain. Other researchers have
noted abnormal patterns of brain activity in patients with schizophrenia. In particular,
these patients suffer from dysfunction of a mechanism known as corollary discharge,
which allows people to distinguish between stimuli outside the self and internal intentions
and thoughts. Electroencephalograms (EEGs) of patients with schizophrenia that were
taken while the patients were talking showed that corollary discharges from the frontal
cortex of the brain (where thoughts are produced) failed to inform the auditory cortex
(where sounds are interpreted) that the talking was self-generated. This failure would lead
the patients to interpret internal speech as coming from external sources, thus producing
auditory hallucinations. In addition, the brains of patients with schizophrenia appear to
suffer tissue loss in certain regions. In early 2004, some German researchers reported a
direct correlation between the severity of auditory hallucinations in patients with
schizophrenia and the amount of brain tissue that had been lost from the primary auditory
cortex.
Diagnosis
The differential diagnosis of hallucinations can be complicated, but in most cases taking
the patient's medical history will help the doctor narrow the list of possible diagnoses. If
the patient has been taken to a hospital emergency room, the doctor may ask those who
accompanied the patient for information. The doctor may also need to perform a medical
evaluation before a psychiatric assessment of the hallucinations can be made. The
medical evaluation may include laboratory tests and imaging studies as well as a physical
examination, depending on the patient's other symptoms. If it is suspected that the patient
is suffering from delirium, dementia, or a psychotic disorder, the doctor may assess the
patient's mental status by using a standard instrument known as the mini-mental status
examination (MMSE) or the Folstein (after the clinician who devised it). The MMSE
yields a total score based on the patient's appearance, mood, cognitive skills, thought
content, judgment, and speech patterns. A score of 20 or lower usually indicates delirium,
dementia, schizophrenia, or severe depression.
Hallucinations in elderly patients may require specialized evaluation because of the
possibility of overlapping causes. The American Association for Geriatric Psychiatry lists
hallucinations as an indication for consulting a geriatric psychiatrist. In addition, elderly
patients should be routinely screened for visual or hearing impairments.
Treatment

11. Hallucinations are treated with regard to the underlying disorder. Depending on the
disorder, treatment may involve antipsychotic, anticonvulsant, or antidepressant
medications; psychotherapy; brain or ear surgery; or therapy for drug dependence.
Hallucinations related to normal sleeping and waking are not a cause for concern.
Prognosis
The prognosis of hallucinations depends on the underlying cause or disorder.
Resources
BOOKS
Altman, Lawrence K., MD. Who Goes First? The Story of Self-Experimentation in
Medicine. Berkeley, CA: University of California Press, 1998.
American Psychiatric Association. Diagnostic and Statistical Manual of Mental
Disorders, 4th edition, text revision. Washington, DC: American Psychiatric Association,
2000.
Beers, Mark H., MD. "Behavior Disorders in Dementia." The Merck Manual of
Geriatrics, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station,
NJ: Merck Research Laboratories, 2002.
"Drug Use and Dependence." The Merck Manual of Diagnosis and Therapy, edited by
Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research
Laboratories, 2002.
Matthiessen, Peter. The Snow Leopard. New York: Penguin Books USA, 1987.
"Psychiatric Emergencies." The Merck Manual of Diagnosis and Therapy, edited by
Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research
Laboratories, 2002.
"Schizophrenia and Related Disorders." Section 15, Chapter 193 in The Merck Manual of
Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD.
Whitehouse Station, NJ: Merck Research Laboratories, 2002.
PERIODICALS
Braun, Claude M. J., Mathieu Dumont, Julie Duval, et al. "Brain Modules of
Hallucination: An Analysis of Multiple Patients with Brain Lesions." Journal of
Psychiatry and Neuroscience 28 (November 2003): 432–439.
Cameron, Scott, MD, and Michael Richards, MD. "Hallucinogens." eMedicine. Cited
January 9, 2004 (March 23, 2004). http://www.emedicine.com/med/topic3407.htm.

12. Chuang, Linda, MD, and Nancy Forman, MD. "Mental Disorders Secondary to General
Medical Conditions." eMedicine. Cited January 30, 2003 (March 23, 2004).
http://www.emedicine.com/med/topic3447.htm.
Cowell, Alan. "Swedish Foreign Minister's Killer Blames 'Voices' in His Head." New
York Times. Cited January 15, 2004.
Ford, J. M., and D. H. Mathalon. "Electrophysiological Evidence of Corollary Discharge
Dysfunction in Schizophrenia During Talking and Thinking." Journal of Psychiatric
Research 38 (January-February 2004): 37–46.
Gaser, C., I. Nenadic, H. P. Volz, et al. "Neuroanatomy of 'Hearing Voices': A
Frontotemporal Brain Structural Abnormality Associated with Auditory Hallucinations in
Schizophrenia." Cerebral Cortex 14 (January 2004): 91–96.
Gleason, Ondria C., MD. "Delirium." American Family Physician 67 (March 1, 2003):
1027–1034.
Ohayon, M. M. "Prevalence of Hallucinations and Their Pathological Associations in the
General Population." Psychiatry Research 97 (December 27, 2000): 153–164.
Pelak, V. S., and G. T. Liu. "Visual Hallucinations." Current Treatment Options in
Neurology 6 (January 2004): 75–83.
Rovner, Barry R., MD. "The Charles Bonnet Syndrome: Visual Hallucinations Caused by
Vision Impairment." Geriatrics 57 (June 2002): 45–46.
Schneider, L. S., and K. S. Dagerman. "Psychosis of Alzheimer's Disease: Clinical
Characteristics and History." Journal of Psychiatric Research 38 (January-February
2004): 105–111.
Tsai, M. J., Y. B. Huang, and P. C. Wu. "A Novel Clinical Pattern of Visual
Hallucination After Zolpidem Use." Journal of Toxicology: Clinical Toxicology 41 (June
2003): 869–872.
OTHER
National Institute of Mental Health (NIMH). Schizophrenia. NIH Publication No.
02-3517. Bethesda, MD: NIMH, 2002. (March 23, 2004).
http://www.nimh.nih.gov/publicat/schizoph.cfm.
National Institute on Drug Abuse (NIDA). Research Report: Hallucinogens and
Dissociative Drugs. NIH Publication No. 01-4209. Bethesda, MD: NIDA, 2001.
ORGANIZATIONS

13. American Academy of Neurology (AAN). 1080 Montreal Avenue, Saint Paul, MN
55116. (651) 695-2717 or (800) 879-1960; Fax: (651) 695-2791.
memberservices@aan.com. http://www.aan.com.
American Association for Geriatric Psychiatry. 7910 Woodmont Avenue, Suite 1050,
Bethesda, MD 20814-3004. (301) 654-7850; Fax: (301) 654-4137.
main@aagponline.org. http://www.aagponline.org.
American Psychiatric Association (APA). 1000 Wilson Boulevard, Suite 1825,
Arlington, VA 22209-3901. (703) 907-7300. apa@psych.org. http://www.psych.org.
National Institute of Mental Health (NIMH) Office of Communications. 6001 Executive
Boulevard, Room 8184, MSC 9663, Bethesda, MD 20892-9663. (301) 443-4513 or (866)
615-NIMH; Fax: (301) 443-5158. nimhinfo@nih.gov. http://www.nimh.nih.gov.
National Schizophrenia Foundation. 403 Seymour Avenue, Suite 202, Lansing, MI
48933. (517) 485-7168 or (800) 482-9534; Fax: (517) 485-7180.
inquiries@nsfoundation.org. http://www.nsfoundation.org.
National Sleep Foundation (NSF). 1522 K Street NW, Suite 500, Washington, DC 20005.
(202) 347-3471; Fax: (202) 347-3472. nsf@sleepfoundation.org.
http://www.sleepfoundation.org.
Rebecca Frey, PhD
Sci-Tech Encyclopedia:
Hallucination
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A perceptual experience in the absence of external stimulation. Hallucinations differ from
illusions, which are changes in the perception of a real object. Hallucinations tend to fade
with fixation or with attention to the content. Except for afterimages, which lie like a film
over objects, hallucinations replace objects and object space. A hallucination is not
objectlike in its realness. The conviction of reality is due to the loss of an object for
comparison and the inability to disprove the image through other sensory modalities.
Hallucinations that are recognized as such by the experiencer include those resulting from
sensory deprivation, drug use, and the phantom limb state. See also Schizophrenia.
Hallucinations may occur in a range of neurologic and psychiatric conditions, although
they are usually considered hallmarks of schizophrenia. Delusional misidentification

14. syndromes are subtype of hallucinations and may also occur in neurological and
psychiatric disease. For example, Capgras syndrome, which is commonly seen in
schizophrenia, causes the individual to replacea familiar person (usually the spouse) with
an imposter with the same or similar physical appearance. Frégoli syndrome is the
delusional confusion of an individual as a familiar person in disguise.
Neurotransmitters are directly involved in the regulation of drug-induced and
schizophrenic hallucinations, with many accounts pointing to the involvement of
serotonin and dopamine. Therefore, it is possible to treat individuals with antipsychotic
drugs that stabilize the chemical systems involved.
With localized damage to the brain, hallucinations are usually brief and intermittent,
though in some cases, especially neurologic damage involving the brainstem,
hallucinations can be chronic and sustained.
Physical input to the eyes and ears constrains and guides the construction of mental
images,but the final result—the perception of an object or sound as a meaningful event
occurringin the external world—also reflects very complex physiological processes. They
begin in the brainstem, pass to the limbic system of the brain, and finally involve the
temporal, parietal, and occipital areas of the cerebral cortex. Various types of
hallucination are caused by disruptions that occur at different levels along that sequence
of brain processes. See also Cognition.
At its earliest phase, damage to the upper brainstem produces peduncular (crepuscular)
hallucinations of faces, torsos, and occasionally geometric patterns or landscapes near the
viewer at the close of day. The images may be static and immobile or may change in
content and affective tonality while being viewed. A smiling young boy, for example,
may change into a scowling oldwoman. The hallucinations are often vivid and chromatic,
and tend to be multimodal: they are seen, heard, and even touched, and occur over the
entire visual field. Olfactory and gustatory images have also been described. Peduncular
hallucinations are similar to the hypnagogic hallucinations that are experienced when
falling asleep. See also Sleep and dreaming.
Neurologic damage involving limbic and temporal-lobe structures yields hallucinations
of faces or formed scenes laden with meaning and affect. Changes in size (micropsia,
macropsia) and shape (metamorphopsia) may occur. Déjà vu, derealization, and dreamy
states are common. Auditory hallucinations are usually of speech or music. Microscopic
(Lilliputian) and autoscopic (out-of-the-body) hallucinations also occur with temporal-
lobe lesions. Exposure to a wide range of drugs and many psychiatric disorders,
especially schizophrenia, can lead to hallucinations whose form suggests dysfunction
involving limbic or temporal-lobe structures. See also Psychotomimetic drug.
Damage to the parietal lobe leads to illusory distortions of shape, size, and motion,
whereas occipital lesions or stimulation—or migraine—gives elementary hallucinations
of sparks, flames, lines, or simple patterns. These hallucinations share features with

15. afterimages.Palinopsia, the hallucinatory persistence of an object after the viewer has
turned away, is a form of pathological afterimagery. See also Perception.
World of the Body:
hallucination
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Hallucination may be simply defined as the perception of an external object in the
absence of a corresponding stimulus, yet such a simple definition obscures a whole series
of conceptual difficulties which surround the medical and psychiatric use of the term. The
range of conditions subsumed under this category is massive, and includes such varied
phenomena as religious visions, phantom limbs, tinnitus, psychedelic ‘trips’,
schizophrenic inner voices, the personal experience of doppelgangers, and a sceptical
apprehension of the unreality of the outer world.
Such variety has naturally frustrated any attempt at providing a clear classification of the
phenomenon. Attempts to distinguish the various forms of hallucination according to
their origins, their content, their intensity, and the condition of their hosts have been
largely unsuccessful. Most psychiatrists in Europe and North America have now adopted
a fairly broad definition of the phenomenon, simply relying upon the distinction between
illusion, which resulted from the misinterpretation of an existing external object, and
hallucination, in which the false perception is generated without any reference to the
outside world. Even this definition, which was introduced by the French psychiatrist J. E.
D. Esquirol in the early nineteenth century, fails to account for such borderline
phenomena as synaesthesia in which the sensations provoked by an object become
confused, so that the subject may taste colours or see sounds.
Alongside this ongoing contest over the definition and classification of hallucination
there exists a more fundamental struggle over the meaning and significance of the
phenomenon. Artists and mystics have long criticized the modern medicalization of
hallucinations, portraying the process as a secularizing attempt to pathologize religious or
spiritual experience. Certainly popular attitudes to hallucination have been transformed
across the last thousand years. In the Platonic tradition of classical philosophy, the
subjective vision was celebrated as a form of privileged insight beyond the phenomenal
experience of the external world. Likewise in the Christian and Jewish religions the
objective quality of the inner hallucination had long been regarded as a proof of its
spiritual reality, although its origin could have been either demonic or divine.
These Platonic and Christian traditions were united in the work of the Primitive Church
fathers. Their writing held up the visionary experience as a charism, a gift from God
which allowed individuals to perceive some object which was normally invisible to men.
This conception was further refined by St Augustine, who divided visions into three
classes: the corporeal, in which an apparition of an object was presented before the
individual's eyes through either natural or spiritual means; the imaginative, in which an

16. image was supernaturally created in the host's mind; and the intellectual, in which sense
of personal assurance was created directly by God, without recourse to implanted words
or images.
This framework for interpreting the hallucinatory experience persisted into the nineteenth
century. Many romantic writers, such as Coleridge and Wordsworth, complained that
normal vision enslaved the mind to the mundane world of material object. In contrast,
they proposed a ‘Spiritual Optics’ (to borrow Thomas Carlyle's phrase) in which the inner
eye would be awakened to the creative inspiration of the spirit. Such a programme sat
unhappily with contemporary medical investigations in this field. In the late eighteenth
and early nineteenth centuries, many writers commented upon the correlation between
hallucination, injury, and disease. This correlation suggested that the hallucination had a
somatic basis, originating in either the disordered operations of the peripheral nerves or
an aberrant psychological process in the brain.
This interpretation of hallucination as a symptom of organic nervous disorder persisted
throughout the nineteenth century. In 1881 the Italian psychiatrist, August Tamburini,
presented a coherent neurological model for the experience, arguing that hallucination
was produced through a pathological excitement or epilepsy in the higher sensory centres
of the brain. This materialist account did little to diminish the mystical celebration of
hallucination. Writers influenced by spiritualism and the Swedish mystic Emanuel
Swedenborg accepted the scientific identification of hallucination with organic
disturbance, arguing that this identity provided strong evidence for the objective reality of
visions.
The mystical assessment of the significance of hallucinations was undermined by a series
of psychological surveys at the end of the nineteenth century. During the 1880s the
statistician, Francis Galton, circulated questionnaires on mental imagery to schools and
acquaintances. From the responses he was able to demonstrate a gradation between
hallucination and the familiar acts of visualization which occurred in everyday life.
Galton suggested that hallucination was not a distinct experience, but rather that it
represented an extreme point on two axes representing the strength of the mental image
and its resistance to conscious control. This statistical erosion of the boundary between
normal visualization and pathological hallucination was reinforced in a more wide-scale
survey published by the Society for Psychical Research (SPR) in 1892. The SPR's
‘Census of Hallucinations’ discovered 1684 cases of waking hallucination amongst 17
000 respondents. Further analysis suggested that hallucination was most prevalent
amongst women, children, and the insane, although the experience could occur in almost
any individual.
In the twentieth century the hallucinatory experience seems to have lost its spiritual
significance. The popular use of hallucinogenic drugs, such as LSD and psilocybin, and
increased understanding of the chemical mechanisms of their actions, has encouraged a
more instrumental attitude towards the visionary experience. Hallucination is no longer
seen as a gratuitous event except in pathological cases such as fever or schizophrenia.
Rather it is a state which can be induced directly through chemical, electrical, or

17. mechanical means. As the neurosurgeon Wilder Penfield demonstrated, intense mental
images may be created through the electrical stimulation of a subject's brain. Likewise
hallucinations of movement (see proprioception) can be induced at a particular joint
through the mechanical vibration of the muscles attached to it. Through such technical
advances the meaning and cultural significance of hallucination has been transformed.
The vision, which once revealed the mind of God to men, is now seen as a symptom
revealing the disordered mind of man to others.
— Rhodri Hayward
Bibliography
• Berrios, G. E. (1995). The history of mental symptoms. Cambridge University
Press, Cambridge.
• Critchley, M. (1987). Hallucinations and their impact upon art. Carnegie Press,
Preston
See also illusions.
Thesaurus:
hallucination
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noun
1. An erroneous perception of reality: delusion, ignis fatuus, illusion, mirage,
phantasm, phantasma, will-o'-the-wisp. See real/imaginary.
2. An illusion of perceiving something that does not really exist: phantasmagoria,
phantasmagory. Slang trip. See real/imaginary.
Antonyms:
hallucination
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n
Definition: dream, delusion
Antonyms: experience, fact, reality, truth

18. Dental Dictionary:
hallucination
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(həl-ōō′sin-ā′shən)
n
An artificial sensory experience without the presence of an external cause.
Philosophy Dictionary:
hallucination
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The occurrence of an experience in itself indistinguishable from a perception of
something, but without an appropriate external cause. Hallucination is sometimes
distinguished from pseudohallucination, in which the experience occurs but is not
mistaken for the perception of an external object. Both are distinct from illusion, in which
there is an external source, but its nature is mistaken (a mirage is thus an illusion, but not
a hallucination). The possibility of hallucination is a frequent starting-point for the
distinction between appearance and reality. See also illusion, argument from.
Columbia Encyclopedia:
hallucination
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hallucination, false perception characterized by a distortion of real sensory stimuli.
Common types of hallucination are auditory, i.e., hearing voices or noises and visual, i.e.,
seeing people that are not actually present. Hallucinations play a prominent role in
schizophrenia and in the mania stage of bipolar disorder (see depression). They are also
significant during withdrawal from various drugs, particularly depressants such as
barbiturates, heroin, and alcohol (see delirium tremens), and under the influence of
hallucinogenic drugs such as LSD, mescaline, and psylocybin. Hallucinations may occur
in normal people under conditions of sensory deprivation, emotional stress, religious
exaltation, or great fatigue.
Law Dictionary:
Hallucination
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19. A state of mind whereby a person senses something that in reality does not exist; a
perception of an object having no reality. 90 S.E. 2d 593, 596. Any of the senses may be
involved, although sight or hearing are most commonly affected. The state of
hallucination most often results from mental illness or from ingesting drugs designed to
create these perceptions. See controlled substance [hallucinogens].
Occultism & Parapsychology Encyclopedia:
Hallucination
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A false perception of sensory vividness arising without the stimulus of a corresponding
sense impression. In this it differs from illusion, which is merely the misinterpretation of
an actual sense perception. Visual and auditory hallucinations are the most common, but
hallucinations of the other senses may also be experienced. Human figures and voices
most frequently form the subject of a hallucination, but in certain types other classes of
objects may be seen, as, for instance, the rats and insects of delirium tremens.
Although hallucination is often associated with various mental and physical diseases, it
may nevertheless occur spontaneously while the agent shows no departure from full vigor
of body and mind. It may also be induced (i.e., in hypnotism) in a high percentage of
subjects. The essential difference between sane and insane hallucinations is that in the
former case the agent can, by reflection, recognize the subjective nature of the
impression, even when it has every appearance of objectivity, whereas in the latter case
the patient cannot be made to understand that the vision is not real.
Until the early twentieth century, hallucinatory percepts were regarded merely as
intensified memory images; however, the most intense of ordinary representations do not
possess the sensory vividness of the smallest sensation received from the external world.
It follows that other conditions must be present besides the excitement of the brain, which
is the correlate of representation. The seat of excitement is the same in actual sense
perceptions and in memory images, but in the former the stimulus is peripherally
originated in the sensory nerve, whereas in the latter it originates in the brain itself.
When a neural system becomes highly excited—a state which may be brought about by
emotion, ill health, drugs, or a number of other causes—it may serve to divert from their
proper paths any set of impulses arising from the sense organs. Because any impulse
ascending through the sensory nerves produces an effect of sensory vividness—normally,
a true perception—the impulses thus diverted gives to the memory image an appearance
of actuality not distinguishable from that produced by a corresponding sense impression
—a hallucination.
In hypnosis a state of cerebral dissociation is induced, whereby a neural system may be
abnormally excited and hallucination thus readily engendered. Drugs, especially
hallucinogens, which excite the brain, also induce hallucinations.

20. In 1901 the British physician Sir Henry Head demonstrated that certain visceral disorders
produce hallucinations, such as the appearance of a shrouded human figure. The question
of whether there is any relationship between the hallucination and the person it represents
is, and has long been, a vexing one. Countless well-authenticated stories of apparitions
coinciding with a death or some other crisis are on record and would seem to establish
some causal connection between them. In former times apparitions were considered to be
the doubles or "ethereal bodies" of real persons, and Spiritualists believe that they are the
spirits of the dead (or, in some instances, of the living) temporarily forsaking the physical
body.
The dress and appearance of the apparition does not necessarily correspond with the
actual dress and appearance of the person it represents. Thus a man at the point of death,
in bed and wasted by disease, may appear to a friend miles away as if in ordinary health
and wearing familiar clothing. Nevertheless, there are notable instances where some
remarkable detail of dress is reproduced in the apparition. It seems clear, however, that it
is the agent's general personality that is, as a rule, conveyed to the percipient, and not,
except in special cases, his or her actual appearance.
It has been suggested that those images that do not arise in the subliminal consciousness
of the agent may be telepathically received by him or her from other minds. A similar
explanation has been offered for the hallucinatory images that many people can induce by
crystal gazing or staring into a pool of water, a drop of ink, or a magic mirror in search of
information about scenes or people they know nothing about.
Collective hallucination is a term applied to hallucinations shared by a number of people.
There is no firm evidence, however, of the operation of any agency other than suggestion
or telepathy.
Hallucination and Psychical Research
One of the most succinct definitions of hallucination occurs in Phantasms of the Living (2
vols., 1886), by Edmund Gurney, F. W. H. Myers, and Frank Podmore: "percepts which
lack, but which can only by a distinct reflection be recognised as lacking, the objective
basis which they suggest." If the sensory perception coincides with an objective
occurrence or counterpart, the hallucination is called veridical, (truth-telling), as in the
phantasm of the dying. If the apparition is seen by several people at the same time, the
case is called collective veridical hallucination.
In the years following the foundation of the Society for Psychical Research (SPR),
London, the hallucination theory of psychic phenomena was in great vogue. If no other
explanation was available the person who had had a supernormal experience was told it
was a hallucination, and if several people testified to the same occurrence it was said that
the hallucination of one was communicated to the others. Sir William Crookes counters
that idea in his Researches in the Phenomena of Spiritualism (1870): "The supposition
that there is a sort of mania or delusion which suddenly attacks a whole roomful of
intelligent persons who are quite sane elsewhere, and that they all concur, to the minutest

21. particulars, in the details of the occurrences of which they suppose themselves to be
witnesses, seems to my mind more incredible than even the facts which they attest."
Charles Richet, in Thirty Years of Psychical Research (1923), omits hallucination
completely in his discussion of metapsychical phenomena (a term for paranormal). He
believed that hallucination should be reserved to describe a morbid state when a mental
image is exteriorized without any exterior reality. According to Richet, "It is extremely
rare that a person who is neither ill, nor drunk, nor hypnotised should, in the walking
state, have an auditory, visual, or tactile illusion of things that in no way exist. The
opinion of alienists that hallucination is the chief sign of mental derangement, and the
infallible characteristic of insanity seems to me well grounded. With certain exceptions
(for every rule there are exceptions) a normal healthy individual when fully awake does
not have hallucinations. If he see[s] apparitions these correspond to some external reality
or other. In the absence of any external reality there are no hallucinations but those of the
insane and of alcoholics."
An instance recounted by Sir John Herschel did not conform to Richet's idea. He had
been watching with some anxiety the demolition of a familiar building. On the following
evening, in good light, he passed the spot where the building had stood. "Great was my
amazement to see it," he wrote, "as if still standing, projected against the dull sky. I
walked on, and the perspective of the form and disposition of the parts appeared to
change as they would have done if real."
In the case of hauntings where a ghost is seen, Gurney suggests that a person thinking of
a given place that is at the time actually experienced in sense perception by others may be
imparting into the consciousness of the others a thought existing in his own.
Of course, data provided by a registering apparatus or photography may rule out the
hallucination theory as applied to hauntings, provided that there is some proper scientific
control. Similarly, if objects are displaced, as in poltergeist cases, the theory of
hallucination is no longer tenable. As Andrew Lang writes in Cock Lane and Common
Sense (1896), "Hallucinations cannot draw curtains, or open doors, or pick up books, or
tuck in bedclothes or cause thumps."
The things seen during a psychic experience of an otherwise normal person should also
be distinguished from the hallucinations of the mentally deranged, of the sick, drunk, or
drugged. The latter are not veridical, nor telepathic, nor collective. In the "Census of
Hallucinations," published in the Proceedings of the SPR (1894), the committee
excluded, as far as possible, all pathological subjects. J. G. Piddington (see Proceedings,
vol. 19), in testing this census for cases that would show the same nature as
hallucinations arising from visceral diseases, concluded that there was not a single case in
the census report that fell into line with the visceral type.
In hypnotic hallucinations the hypnotized subject may see apparitions if so suggested and
may not see ordinary people who are in the same room. But the subject may hear the
noises they make, see the movement of objects they touch, and be frightened by what

22. appears to be poltergeist phenomena. If the suggestion is posthypnotic the subject may
also see a phantom shape when given a signal or at a prescribed time.
The visions seen by some people on the verge of sleep were called " hypnagogic
hallucinations" by F. W. H. Myers. The afterimages on waking from sleep he named
"hypnopompic hallucinations." A comprehensive study of both classes of phenomena
was published by G. E. Leaning in the Proceedings of the SPR, (vol. 35, 1926).
The difference between hallucination and illusion is that there is an objective basis for the
illusion, which is falsely interpreted. In hallucination, although more than one sense may
be affected, there is no external basis for the perception.
Sources:
Besterman, Theodore. Crystal-Gazing. London, 1924. Reprint, New Hyde Park, NY:
University Books, 1965.
Bramwell, J. M. Hypnotism: Its History, Practice, and Theory. London, 1903.
Gurney, Edmund, F. W. H. Myers, and Frank Podmore. Phantasms of the Living. 2 vols.
London: Trubner, 1886. Reprint, Gainesville, FL: Scholars Facsimiles Reprints, 1970.
Huxley, Aldous. The Doors of Perception. London, 1954. Johnson, Fred H. The Anatomy
of Hallucinations. Chicago: Nelson Hall, 1978.
MacKenzie, Andrew. Apparitions and Ghosts. London: Barker, 1971. Reprint, New
York: Popular Library, 1972.
——. Hauntings and Apparitions. London: Heinemann, 1982.
Myers, F. W. H. Human Personality and Its Survival of Bodily Death. 2 vols. London:
Longmans Green, 1903. Reprint, New York: Arno Press, 1975.
Podmore, Frank. Apparitions and Thought Transference. London, 1894.
Reed, Graham. The Psychology of Anomalous Experience. Boston: Houghton Mifflin,
1974.
Richet, Charles. Thirty Years of Psychical Research. London: W. Collins, 1923. Reprint,
New York: Arno Press, 1975.
Rogo, D. Scott. Mind Beyond the Body: The Mystery of ESP Projection. New York:
Penguin, 1978.
Samuels, Mike. Seeing With the Mind's Eye: The History, Techniques, and Uses of
Visualization. New York: Bookworks; Random House, 1975.

23. Tyrrell, G. N. M. Apparitions. London: Duckworth, 1953. Reprint, London: Society for
Psychical Research, 1973.
World of the Mind:
hallucination
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Briefly defined as sensory perception in the absence of external stimuli, hallucination has
three characteristics: thoughts or memory images, perhaps when they are as vivid and
immediate as perceptions, are experienced as if they were perceptions; they are
externalized, or projected, being experienced as if they came from outside the person; and
the mistaking of imagery for perception is not corrected in the light of the other
information available. The term pseudohallucination has been used to describe imagery
as vivid and immediate as perception but not mistaken as such. Pseudohallucinations are
more likely to be perceived in response to isolation or an intense emotional need: for
example, shipwrecked sailors may visualize boats coming to their rescue. The fanciful
elaboration of perception of external stimuli — for example, faces seen in the fire — is
illusion. The imagery of a vision is experienced as if it came from outside, although not
from ordinary reality as perception does.
Young children often fail to distinguish between imagery and perception and suppose that
what they imagine is external and perceptible to others. Adults sometimes fail to make
the distinction, especially at a time of high expectation or arousal. A widow mourning her
husband may see him or hear his voice or footsteps repeatedly after his death, resulting in
a 'sense of presence' which fades with the passage of time. In a wood at night, dark
shadows are seen as lurking beasts. Waking from a frightening dream, a person feels that
what he has experienced has happened in reality.
Mistakes like these are corrected when the person recognizes that they conflict with other
information or the views of others. Normally imagery is continually reappraised in the
light of further information becoming available, and further information is sought by
testing reality. Hearing a noise, a person makes a small head movement and tests whether
the change in the strength and character of the noise conforms to his expectation.
Perceiving someone in a crowd as an acquaintance, a person looks again or asks a
companion for confirmation. Macbeth in Shakespeare's play, while planning to murder
Duncan, hallucinates a dagger, and asks: 'Art thou not, fatal vision, sensible to feeling as
to sight? Or art thou but a dagger of the mind, a false creation, proceeding from the heat-
oppressed brain?'
After a long period of wakefulness or busyness, attention tends to be withdrawn from the
outside world, and the testing of reality to be impaired and reduced. Hallucination is
relatively common under these conditions and remains uncorrected for longer. Sufficient
information is available but is not used. On the other hand, the subjects of experiments on
the effects of sensory deprivation, who are put into a darkened and soundproofed room,
do not get sufficient information to enable them to test reality and to reappraise their

24. hallucinatory experiences. (See isolation experiments.) Also, a person on his own is less
able to test reality and to reappraise what he has experienced.
Hallucinations tend to be disowned, the person feeling that he has no control over the
imagery, which he feels is imposed on him by an outside agency. They are often reported
as distressing, threatening, or tormenting, only occasionally, for example by a widow, as
reassuring. There are other distressing phenomena that are not hallucinations, although
akin to them in some respects. Thus, some recurring images obtrude and cannot be
stopped, but are accepted as belonging to the individual. Such images are termed
obsessions. Ringing in the ear ('tinnitus'), resulting, for instance, from disease of the ear,
is sometimes described by a fanciful simile, e.g. as being like sea flowing over shingle, or
as if there were nearby a machine crushing stones. What is being described may be
thought mistakenly to be hallucination if the explicit comparison of the 'like' or the 'as if'
fails to be noted.
Hallucination is common in patients who have suffered damage to the brain as a result of
trauma, infection, or intoxication by drugs or alcohol. The association of hallucination,
fearfulness, and agitation in these cases may be described as delirium. A patient who
suffers from delirium tremens as a result of alcoholism may see such frightening things as
red spiders or pink elephants, or he may feel that lice are crawling over his skin, because
hallucination although usually visual may be experienced through any of the senses.
Indeed, hallucinations in functional psychoses are more often auditory than visual.
Schizophrenic patients may hear the voices of their persecutors, conversations about
themselves between third parties, or their own thoughts spoken aloud (echo de pensée).
Severely depressed patients may hear voices making derogatory remarks or threatening
them with punishment or torture. Some schizophrenic patients even experience tactile
hallucinations which give rise to delusional beliefs that they are being sexually assaulted.
Olfactory hallucinations are sometimes perceived by severely melancholic patients who
come to believe that they are giving off revolting odours from their bodies causing people
to avoid them. Patients mistake hallucinations of all these kinds for perceptions coming
from outside themselves, and attribute to others what they experience, usually without
any testing of reality.
Explanations of hallucination refer to several processes. In delirium there tends to be a
high level of arousal and at the same time a lowering of vigilance, impairment of
perception, and impairment and reduction of reality testing. Enhancement of imagery as a
direct effect of drugs or toxins on nervous tissue is similar to that of electrical stimulation
of the temporal lobes of the brain when it produces, in a conscious patient whose brain
has been exposed during surgery, intense visual, auditory, or other imagery as 'strips' of
experience. Poisoning by drugs may also, more importantly, increase the random activity
of nervous tissue. Sensations then become blurred, to produce background noise, which is
then elaborated into illusion. A person poisoned by LSD may see visual patterns like lace
curtains, usually coloured. In some illnesses in which there is hallucination, the
functioning of peripheral nerves is affected by neuritis, and as a result the patient may
experience numbness, pins and needles, or itching, which is elaborated into the illusion of
lice. Similarly, the result of neuritis of the retina may be spiders dangling in front of the

25. eyes, brain-elaborations of phosphenes. In schizophrenia, the patient has typically
disengaged from social activities, and the testing of reality is reduced as a result, but this
does not account for his disowning of what he experiences. It has to be supposed that
thoughts and feelings have been dissociated as a psychological defence in order to reduce
the anxiety which would otherwise arise. The patient positively resists any reappraisal of
what he has experienced.
(Published 1987)
— Derek Russell Davis
Bibliography
• Galton, F. (1907). Inquiries into Human Faculty and its Development.
• Harris, J. P., and Gregory, R. L. (1981). 'Tests of hallucinations of Ruth'.
Perception, 10.
• Siegel, R. K. (1993). Fire in the Brain: Clinical Tales of Hallucination.
• — — and West, J. L. (eds., 1975). Hallucinations.
Word Tutor:
hallucination
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IN BRIEF: Something that is not real but of which someone is aware.
Someone who travels in the desert might have a hallucination of a swimming pool.
LearnThatWord.com is a free vocabulary and spelling program where you only pay for
results!
Science Dictionary:
hallucination
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A false perception that appears to be real, as when, for example, a man dying of thirst in a
desert thinks that he sees a lake. (See also delusion.)

26. Wikipedia:
Hallucination
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For other uses, see Hallucination (disambiguation).
Hallucination
A hallucination, in the broadest sense, is a perception in the absence of a stimulus. In a
stricter sense, hallucinations are defined as perceptions in a conscious and awake state in
the absence of external stimuli which have qualities of real perception, in that they are
vivid, substantial, and located in external objective space. The latter definition
distinguishes hallucinations from the related phenomena of dreaming, which does not
involve wakefulness; illusion, which involves distorted or misinterpreted real perception;
imagery, which does not mimic real perception and is under voluntary control; and
pseudohallucination, which does not mimic real perception, but is not under voluntary
control.[1] Hallucinations also differ from "delusional perceptions", in which a correctly
sensed and interpreted genuine perception is given some additional (and typically bizarre)
significance.
Hallucinations can occur in any sensory modality — visual, auditory, olfactory,
gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and
chronoceptive.
A mild form of hallucination is known as a disturbance, and can occur in any of the
senses above. These may be things like seeing movement in peripheral vision, or hearing
faint noises and/or voices. Auditory hallucinations are very common in schizophrenia of
the paranoid type. They may be benevolent (telling the patient good things about himself)
or malicious, cursing the patient etc. Auditory hallucinations of the malicious type are
frequently heard like people talking about the patient behind his back. Like auditory
hallucinations, the source of their visual counterpart can also be behind the patient's back.
Their visual counterpart is the feeling of being looked-stared at, usually with malicious
intent. Not infrequently, auditory hallucinations and their visual counterpart are
experienced by the patient together.
Hypnagogic hallucinations and hypnopompic hallucinations are considered normal
phenomena. Hypnagogic hallucinations can occur as one is falling asleep and
hypnopompic hallucinations occur when one is waking up.

27. Hallucinations can also be associated with drug or alcohol use (particularly deliriants),
sleep deprivation, psychosis, neurological disorders, and delirium tremens.
Contents [hide]
• 1 Prevalence
• 2 Hallucination modalities
o 2.1 Visual hallucinations
o 2.2 Auditory hallucinations
o 2.3 Olfactory hallucinations
o 2.4 Tactile hallucinations
• 3 Types of hallucinations
o 3.1 Hypnagogic hallucination
o 3.2 Peduncular hallucinosis
o 3.3 Delirium tremens
o 3.4 Parkinson's disease and Lewy body dementia
o 3.5 Migraine coma
o 3.6 Charles Bonnet syndrome
o 3.7 Focal epilepsy
o 3.8 Schizophrenic hallucination
o 3.9 Drug-induced hallucination
• 4 Scientific explanations
• 5 Stages of a hallucination
• 6 Treatments
• 7 See also
• 8 Notes
• 9 External links
Prevalence
One study from as early as 1894[2] reported that approximately 10% of the population
experienced hallucinations. A 1996-1999 survey of over 13,000 people[3] reported a much
higher figure, with almost 39% of people reporting hallucinatory experiences, 27% of
which were daytime hallucinations, mostly outside the context of illness or drug use.
From this survey, olfactory (smell) and gustatory (taste) hallucinations seem the most
common in the general population.
Hallucination modalities
Hallucinations may be manifested in a variety of forms.[4] Various forms of hallucinations
affect different senses, sometimes occurring simultaneously, creating multiple sensory
hallucinations for those experiencing them.
Visual hallucinations

28. The real shadow of the hallucinating person transforms into the corporal image.
The most common modality referred to when people speak of hallucinations. These
include the phenomena of seeing things which are not present or visual perception which
does not reconcile with the consensus reality. There are many different causes, which
have been classed as psychophysiologic (a disturbance of brain structure),
psychobiochemical (a disturbance of neurotransmitters), and psychological (e.g.
meaningful experiences intruding into consciousness). Numerous disorders can involve
visual hallucinations, ranging from psychotic disorders to dementia to migraine, but
experiencing visual hallucinations does not in itself mean there is necessarily a disorder.[5]
Auditory hallucinations
Main article: Auditory hallucination
Auditory hallucinations (also known as Paracusia),[6] particularly of one or more talking
voices, are particularly associated with psychotic disorders such as schizophrenia or
mania, and hold special significance in diagnosing these conditions, although many
people not suffering from diagnosable mental illness may sometimes hear voices as well.
Auditory hallucinations of non-organic origin are most often met with in paranoid
schizophrenia. their visual counterpart in that disease is the non-reality-based feeling of
being looked or stared at.
Other types of auditory hallucination include exploding head syndrome and musical ear
syndrome, and may occur during sleep paralysis. In the latter, people will hear music
playing in their mind, usually songs they are familiar with. Recent reports have also
mentioned that it is also possible to get musical hallucinations from listening to music for
long periods of time.[7] This can be caused by: lesions on the brain stem (often resulting
from a stroke); also, tumors, encephalitis, or abscesses.[8] Other reasons include hearing
loss and epileptic activity.[9] Auditory hallucinations are also a result of attempting wake-
initiation of lucid dreams.
Olfactory hallucinations
Phantosmia is the phenomenon of smelling odors that aren't really present. The most
common odors are unpleasant smells such as rotting flesh, vomit, urine, feces, smoke, or
other unpleasant smells. Phantosmia often results from damage to the nervous tissue in
the olfactory system. The damage can be caused by viral infection, brain tumor, trauma,
surgery, and possibly exposure to toxins or drugs.[10] Phantosmia can also be induced by
epilepsy affecting the olfactory cortex and is also thought to possibly have psychiatric
origins.[citation needed] Phantosmia is different from parosmia, in which a smell is actually
present, but perceived differently from its usual smell.

29. Olfactory hallucinations have also been reported in migraine, although the frequency of
such hallucinations is unclear.[11][12]
Tactile hallucinations
Other types of hallucinations create the sensation of tactile sensory input, simulating
various types of pressure to the skin or other organs. This type of hallucination is often
associated with substance use, such as someone who feels bugs crawling on them (known
as formication) after a prolonged period of cocaine or amphetamine use.[13]
Types of hallucinations
Hallucinations can be caused by a number of factors.
Hypnagogic hallucination
Main article: Hypnagogia
These hallucinations occur just before falling asleep, and affect a surprisingly high
proportion of the population. The hallucinations can last from seconds to minutes, all the
while the subject usually remains aware of the true nature of the images. These may be
associated with narcolepsy. Hypnagogic hallucinations are sometimes associated with
brainstem abnormalities, but this is rare.[14]
Peduncular hallucinosis
Main article: Peduncular hallucinosis
Peduncular means pertaining to the peduncle, which is a neural tract running to and from
the pons on the brain stem. These hallucinations usually occur in the evenings, but not
during drowsiness, as in the case of hypnagogic hallucination. The subject is usually fully
conscious and then can interact with the hallucinatory characters for extended periods of
time. As in the case of hypnagogic hallucinations, insight into the nature of the images
remains intact. The false images can occur in any part of the visual field, and are rarely
polymodal.[14]
Delirium tremens
Main article: Delirium tremens
One of the more enigmatic forms of visual hallucination is the highly variable, possibly
polymodal delirium tremens. Individuals suffering from delirium tremens may be
agitated and confused, especially in the later stages of this disease. Insight is gradually
reduced with the progression of this disorder. Sleep is disturbed and occurs for a shorter
period of time, with Rapid eye movement sleep.

30. Parkinson's disease and Lewy body dementia
Parkinson's disease is linked with Lewy body dementia for their similar hallucinatory
symptoms. The symptoms strike during the evening in any part of the visual field, and are
rarely polymodal. The segue into hallucination may begin with illusions[15] where sensory
perception is greatly distorted, but no novel sensory information is present. These
typically last for several minutes, during which time the subject may be either conscious
and normal or drowsy/inaccessible. Insight into these hallucinations is usually preserved
and REM sleep is usually reduced. Parkinson's disease is usually associated with a
degraded substantia nigra pars compacta, but recent evidence suggests that PD affects a
number of sites in the brain. Some places of noted degradation include the median raphe
nuclei, the noradrenergic parts of the locus coeruleus, and the cholinergic neurons in the
parabrachial and pedunculopontine nuclei of the tegmentum.[14]
Migraine coma
This type of hallucination is usually experienced during the recovery from a comatose
state. The migraine coma can last for up to two days, and a state of depression is
sometimes comorbid. The hallucinations occur during states of full consciousness, and
insight into the hallucinatory nature of the images is preserved. It has been noted that
ataxic lesions accompany the migraine coma.[14]
Charles Bonnet syndrome
Charles Bonnet syndrome is the name given to visual hallucinations experienced by blind
patients. The hallucinations can usually be dispersed by opening or closing the eyelids
until the visual images disappear. The hallucinations usually occur during the morning or
evening, but are not dependent on low light conditions. These prolonged hallucinations
usually do not disturb the patients very much, as they are aware that they are
hallucinating.[14] A differential diagnosis are opthalmopathic hallucinations [16].
Focal epilepsy
The visual hallucinations from focal epilepsy are characterized by being brief and
stereotyped. They are usually localized to one part of the visual field, and last only a few
seconds. Other epileptic features may present themselves between visual episodes.
Consciousness is usually impaired in some way, but nevertheless, insight into the
hallucination is preserved. Usually, this type of focal epilepsy is caused by a lesion in the
posterior temporoparietal.[14]
Schizophrenic hallucination
Hallucinations caused by schizophrenia.
Drug-induced hallucination

31. Hallucinations caused by the consumption of psychoactive substances.
Scientific explanations
Various theories have been put forward to explain the occurrence of hallucinations. When
psychodynamic (Freudian) theories were popular in psychiatry, hallucinations were seen
as a projection of unconscious wishes, thoughts and wants. As biological theories have
become orthodox, hallucinations are more often thought of (by psychologists at least) as
being caused by functional deficits in the brain. With reference to mental illness, the
function (or dysfunction) of the neurotransmitters glutamate and dopamine are thought to
be particularly important.[17] The Freudian interpretation may have an aspect of truth, as
the biological hypothesis explains the physical interactions in the brain, while the
Freudian deals with the origin of the flavor of the hallucination. Psychological research
has argued that hallucinations may result from biases in what are known as metacognitive
abilities.[18] These are abilities that allow us to monitor or draw inferences from our own
internal psychological states (such as intentions, memories, beliefs and thoughts). The
ability to discriminate between internal (self-generated) and external (stimuli) sources of
information is considered to be an important metacognitive skill, but one which may
break down to cause hallucinatory experiences. Projection of an internal state (or a
person's own reaction to another's) may arise in the form of hallucinations, especially
auditory hallucinations. A recent hypothesis that is gaining acceptance concerns the role
of overactive top-down processing, or strong perceptual expectations, that can generate
spontaneous perceptual output (that is, hallucination).[19]
Stages of a hallucination
1. Emergence of surprising or warded-off memory or fantasy images [20]
2. Frequent reality checks [20]
3. Last vestige of insight as hallucinations become "real" [20]
4. Fantasy and distortion elaborated upon and confused with actual perception [20]
5. Internal-external boundaries destroyed and possible pantheistic experience [20]
Treatments
There are few treatments for many types of hallucinations. However, for those
hallucinations caused by mental disease, a psychologist or psychiatrist should be alerted,
and treatment will be based on the observations of those doctors. Antipsychotic
medications may also be utilized to treat the illness.[21] For other causes of hallucinations
there is no factual evidence to support any one treatment is scientifically tested and
proven. However, abstaining from hallucinogenic drugs, managing stress levels, living
healthily, and getting plenty of sleep can help reduce the prevalence of hallucinations. In
all cases of hallucinations, medical attention should be sought out and informed of one's
specific symptoms.

32. 1. ^ Leo P. W. Chiu (1989). "Differential diagnosis and management of
hallucinations" (PDF). Journal of the Hong Kong Medical Association 41 (3):
292–7. http://sunzi1.lib.hku.hk/hkjo/view/21/2100448.pdf.
2. ^ Sidgwick H, Johnson A, Myers FWH et al. (1894). "Report on the census of
hallucinations". Proceedings of the Society for Psychical Research 34: 25–394.
3. ^ Ohayon MM (Dec 2000). "Prevalence of hallucinations and their pathological
associations in the general population". Psychiatry Res 97 (2-3): 153–64.
doi:10.1016/S0165-1781(00)00227-4. PMID 11166087.
http://linkinghub.elsevier.com/retrieve/pii/S0165178100002274.
4. ^ Chen E. and Berrios G.E. (1996) Recognition of hallucinations: a
multidimensional model and methodology. Psychopathology 29: 54-63.
5. ^ Visual Hallucinations: Differential Diagnosis and Treatment (2009)
6. ^ "Medical dictionary". http://medical-
dictionary.thefreedictionary.com/paracusia.
7. ^ Young, Ken (July 27, 2005). "IPod hallucinations face acid test". Vnunet.com.
http://www.vnunet.com/vnunet/news/2140422/ipod-help-produce-musical.
Retrieved 2008-04-10.
8. ^ "Rare Hallucinations Make Music In The Mind". ScienceDaily.com. August 9,
2000. http://www.sciencedaily.com/releases/2000/08/000809065249.htm.
Retrieved 2006-12-31.
9. ^ Engmann, Birk; Reuter, Mike: Spontaneous perception of melodies –
hallucination or epilepsy? Nervenheilkunde 2009 Apr 28: 217-221. ISSN
0722-1541
10. ^ Phantom smells
11. ^ Wolberg FL, Zeigler DK (1982). "Olfactory Hallucination in Migraine".
Archives of Neurology 39 (6): 382.
12. ^ Sacks, Oliver (1986). Migraine. Berkeley: University of California Press.
pp. 75–76. ISBN 9780520058897.
13. ^ Berrios G E (1982) Tactile Hallucinations. Journal of Neurology, Neurosurgery
and Psychiatry 45: 285-293
14. ^ a b c d e f Manford M, Andermann F (Oct 1998). "Complex visual hallucinations.
Clinical and neurobiological insights". Brain 121 ((Pt 10)): 1819–40. doi:10.1093/
brain/121.10.1819. PMID 9798740.
http://brain.oxfordjournals.org/cgi/content/abstract/121/10/1819.
15. ^ Mark Derr (2006) Marilyn and Me, "The New York Times" February 14, 2006
16. ^ Engmann, Birk (2008). "Phosphenes and photopsias - ischaemic origin or
sensorial deprivation? - Case history" (in German). Z Neuropsychol. 19 (1): 7–13.
doi:10.1024/1016-264X.19.1.7.
http://www.psycontent.com/content/m507n73711u73652/?
p=400b10f998844a6abe524fcf44626323&pi=1.
17. ^ Kapur S (Jan 2003). "Psychosis as a state of aberrant salience: a framework
linking biology, phenomenology, and pharmacology in schizophrenia". Am J
Psychiatry 160 (1): 13–23. doi:10.1176/appi.ajp.160.1.13. PMID 12505794.
http://ajp.psychiatryonline.org/cgi/pmidlookup?view=long&pmid=12505794.
18. ^ Bentall RP (Jan 1990). "The illusion of reality: a review and integration of
psychological research on hallucinations". Psychol Bull 107 (1): 82–95.

33. doi:10.1037/0033-2909.107.1.82. PMID 2404293. http://content.apa.org/journals/
bul/107/1/82.
19. ^ Grossberg S (Jul 2000). "How hallucinations may arise from brain mechanisms
of learning, attention, and volition". J Int Neuropsychol Soc 6 (5): 583–92.
doi:10.1017/S135561770065508X. PMID 10932478.
20. ^ a b c d e Horowitz MJ (1975). "Hallucinations: An Information Processing
Approach". in West LJ, Siegel RK. Hallucinations; behavior, experience, and
theory. New York: Wiley. ISBN 0-471-79096-6.
^ "Hallucinations: Treatment: Information from Answers.com." Answers.com: Wiki
Q&A combined with free online dictionary, thesaurus, and encyclopedias.
http://www.answers.com/topic/hallucinations-treatment (accessed January 20,
Copyrights: Hallucinogens
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Hallucinogens are natural and synthetic (synthesized) substances that, when ingested
(taken into the body), significantly alter one's state of consciousness. Hallucinogenic
compounds often cause people to see (or think they see) random colors, patterns, events,
and objects that do not exist. People sometimes have a a different perception of time and
space, hold imaginary conversations, believe they hear music and experience smells,
tastes, and other sensations that are not real.
Hallucinogen Classification
Many types of substances are classified as hallucinogens, solely because of their capacity
to produce such hallucinations. These substances are sometimes called "pyschedelic," or
"mind-expanding" drugs. They are generally illegal to use in the United States, but are
sometimes sold on the street by drug dealers. A few hallucinogens have been used in
medicine to treat certain disorders, but they must be given under controlled
circumstances. Hallucinogens found in plants and mushrooms were used by humans for
many centuries in spiritual practice worldwide.
Unlike such drugs as barbiturates and amphetamines (which depress or speed up the
central nervous system, respectively) hallucinogens are not physically addictive (habit-
forming). People can become psychologically dependent upon them, however. The real
danger of hallucinogens is not their toxicity (poison level), but their unpredictability.
People have had such varied reactions to these substances, especially to LSD (lysergic
acid diethylamide), that it is virtually impossible to predict the effect a hallucinogen will
have on any given individual. Effects depend upon the person's mood, surroundings,
personality, and expectations when taking the drug.
Hallucinogens and Spirituality
Some users of hallucinogens have reported feeling mystical and insightful, while others
are fearful, paranoid (excessively suspicious or mistrustful of others), and hysterical
(exhibiting overwhelming or unmanageable fear or emotional excitability). Medicine
men, shamans, and other spiritual leaders have used natural hallucinogens found in plants
and mushrooms since ancient times, believing in their power to help contact the spiritual
world or mystical beings for guidance in serving their people.
Pollen from flowers and other plants-—most with medicinal properties-—was found in
the grave of a Neanderthal man in Shanidar, Iraq. Scientists believe that since these
prehistoric people very likely knew how to use plants for medicine, they probably used
hallucinogenic plants in rituals. Archaeological evidence also shows that psychoactive
drugs (drugs that affect the mind or behavior) were used in ancient Egypt, Greece,
Europe, and many other cultures.

35. Natural hallucinogens are formed in dozens of psychoactive plants, including the peyote
cactus, various species of mushrooms, and the bark and seeds of several trees and plants.
In Mexico, mushrooms called Psylocybe mexicana, which contain the fungi psilocybin
and psilocin, have been used in religious rituals since the time of the Aztec civilization
(before 1519, an empire in Central America noted for its advanced social development).
In Europe, the fungus Amanita muscaria was thought to have been used by the Vikings.
Amanita muscaria and its close relative, Amanita pantherina, are also found in the United
States. Both contain psychoactive ingredients called ibotenic acid and muscimol.
LSD crystals. Hallucinogens have been studied for possible medical uses, including the
treatment of some forms of mental illness, alcholism, and addiction to the drug opium.
Some members of the Native American Church, an organization made up of Native
Americans from tribes throughout North America, practice the use of mescaline, a form
of psychedelic drug found in the peyote cactus. Currently peyote is the only psychedelic
agent that has been authorized by the federal government for limited use during Native
American religious ceremonies.
A few less common natural hallucinogens are also used in religious practice. These
include ololiuqui (morning glory) seeds, which are eaten by Central and South American
Indians both as intoxicants (a substance, such as alcohol, that excites or makes one
insensible) and hallucinogens. Harmine, another psychedelic chemical that has been used
for centuries, is obtained from the seeds of Peganum harmala, a plant found in the Middle
East. The feeling of exhilaration (cheerfulness, excitement) brought about by this drug is
sometimes followed by nausea, fatigue, and sleep. People using the drug may experience
visual distortions (for instance, an object appears to be in a different shape from what it
really is) like those induced by LSD.
DMT (dimethyltryptamine)is a hallucinogen found in the seeds of certain West Indian
and South American plants. People in Haiti have used this drug, in the form of a snuff (a
tobacco product inhaled through the nostrils, chewed, or placed against the gums) called
cohoba, in religious ceremonies.

36. Marijuana, LSD, and PCP
Marijuana and hashish, two substances derived from the hemp plant (Cannabis sativa),
are also considered natural hallucinogens, although their potency (power) is very low
when compared to others. Marijuana (also called grass, pot, tea, weed, or reefer), a green
herb from the flower of the hemp plant, is considered a mild hallucinogen. Hashish is
marijuana in a more potent, concentrated form. Both drugs are usually smoked. Their
effects include a feeling of relaxation, faster heart rate, the sensation that time is passing
more slowly, and a greater sense of hearing, taste, touch, and smell.
Even the most potent of these naturally occurring hallucinogens is not nearly as powerful
and unpredictable as the synthetic hallucinogen LSD, which is chemically derived from
ergot, a parasitic fungus (a fungus that lives in or on a host, deriving benefits from the
host while injuring it) that grows on rye and other grains. LSD became well known in the
1960s, when many people sought spiritual enlightenment through the use of drugs.
A form of LSD was first produced in 1938, when Albert Hoffman, a Swiss research
chemist at Sandoz Laboratories, synthesized many important ergot alkaloids (organic
plant bases), including Hydergine, LSD-25, and psilocybin. Hoffman accidentally
experienced the first "LSD high" when a drop of the material entered his bloodstream
through the skin of his fingertip. Hoffman could hardly recount his experience after it
was over. He was the first to record LSD's ability to cause the user to experience
synesthesia, an overflow of one sensory ability into another. For example, a person
experiencing synesthesia may hear colors and see sounds.
The physical effects of hallucinogens are considered small compared to their effects on
the mind. Death from an overdose of hallucinogens is highly unlikely, but deaths have
resulted from accidents or suicides involving people under the influence of LSD. The
drug made them so indifferent to the world around them they thought they could step out
of a window, for example, without harm. LSD is sold on the street in various forms,
sometimes on a piece of paper marked into squares, with each square being one dose.
LSD is so powerful that a tiny amount can have a hallucinogenic effect. Just three pounds
of LSD could cause a reaction in all the people in New York City and London combined.
Because it is so strong and its action so unpredictable, LSD is considered very dangerous.
The drug phencyclidine, or PCP, known as "angel dust" and "rocket fuel," was widely
abused in the late 1970s. PCP is dangerous because it produces a sense of indifference
about the world and a reduced sensitivity to pain. Combined with hallucinogenic effects,
it can result in bizarre thinking and violently destructive behavior.
Taking hallucinogens can cause sweating, excessive salivation, decreased heart rate,
increased blood pressure, and change in pupil size. LSD users may experience flashbacks
of visions they had when on the drug. Some LSD users suffer organic brain damage,
which results in impaired memory and attention span, confusion, and difficulty in
thinking. Some scientists believe hallucinogens affect serotonin, a neurotransmitter (a

37. substance that transmits nerve impulses) in the brain. Recently several hallucinogenic
compounds have been found to resemble serotonin structurally. One theory is that at least
some drug-induced hallucinations are due to changes in the functioning of serotonin
neurons. It was demonstrated that LSD interfered with the transmitter action of serotonin.
Medical Uses of Hallucinogens
Hallucinogens have been studied for possible medical uses, including the treatment of
some forms of mental illness, alcholism, and addiction to the drug opium. They have also
been given to dying patients. Most of these uses have been abandoned, however.
A synthetic form of the active chemical in marijuana, THC, has been approved for
prescription use by cancer patients who suffer from severe nausea after receiving
chemotherapy (treating cancer with drugs). THC is also used to reduce eye pressure in
treating severe cases of glaucoma. PCP is occasionally used by veterinarians as an
anesthetic and sedative for animals.
Read more: Hallucinogens - used, first, anesthetic, blood, body, produced, plant, uses,
Hallucinogen Classification, Hallucinogens and Spirituality, Marijuana, LSD, and PCP
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